1. Field of the Invention
The present invention relates generally to boom and attachment control systems for vehicles. In particular, the present invention is an electronic bucket positioning and control system.
2. Description of the Prior Art
Vehicles such as articulated loaders, skid steer loaders and back hoes are well known. Vehicles of these types typically include a body, a frame or other support structure to which a boom assembly is pivotally mounted. An attachment such as a bucket is pivotally mounted to the boom assembly. A hydraulic system is also typically included for driving the boom assembly and bucket. The hydraulic system can include one or more hydraulic lift cylinders for driving the boom assembly with respect to the support structure, and one or more hydraulic tilt cylinders for driving the bucket with respect to the boom assembly. Through the use of a control handle, an operator will actuate a tilt valve to control the tilt cylinders, and a lift valve to control the lift cylinders. In one conventional system, the operator will push the control handle forward to lower the boom assembly, pull the control handle backward to lift the boom assembly, move the control handle to the left to roll the bucket back, and move the handle to the right to dump or roll the bucket out.
When using hydraulic control systems of the type described above, the operator often repetitively performs many operations. When raising or lowering the boom assembly with a loaded bucket, for example, the operator must constantly make sure that the bucket is kept in a predetermined angular relationship with respect to the vehicle body or support structure to prevent the load from being accidentally spilled. The operator is therefore required to visually monitor the angular position of the bucket, and to adjust the bucket's position relative to the boom assembly while simultaneously raising or lowering the boom assembly. Although hydraulic self-leveling systems are known and disclosed, for example, in the Diel et al U.S. Pat. No. 4,408,518, systems of this type are relatively complicated, and typically work only when the boom assembly is being raised.
Another repetitively performed operation is that of returning the bucket to a predetermined position after it has been rolled out or rolled back. For example, after dumping a load it is typically required to return the bucket to a digging position before another load can be scooped. Known return to position systems include an operator actuated switch which will activate a magnet or other mechanism to hold the tilt valve in a position which will cause the bucket to be rolled back to a position determined by a limit switch mounted on the boom assembly. When the bucket has rolled back and actuates the limit switch, the mechanism holding the tilt valve is released.
The precise rollback position is set by physically adjusting the position of the limit switch. This prior art system, however, only permits the bucket to be returned to one position which is set by the limit switch. In addition, it only permits the bucket to be returned to a predetermined rollback position after being dumped. It is often desirable, however, to vary the position to which the bucket should be returned. It is also often necessary to return the bucket to a predetermined position from a completely rolled back position as well as from a rolled out or dumped position.
Another commonly performed operation is that of actuating the tilt valve to bang the hydraulic tilt cylinder at its end of travel so as to jar debris free from the bucket. This banging results in the pistons of the hydraulic tilt cylinders being forced against stops at the end of the cylinder, and results in unnecessary wear. Although the hydraulic tilt cylinders typically have a hydraulic fluid port spaced from the end of the cylinder thereby preventing hydraulic fluid from rapidly exiting the cylinder when the piston is near the end of its travel limit, and somewhat dampening the forces applied to the cylinder, this mechanism still permits large forces to be applied to the cylinder. This hydraulic cushion system prevents banging which is sometimes needed to jar debris free.
It is evident that there is a continuing need for improved boom and bucket control systems for vehicles of this type described above. A system capable of maintaining the bucket at any desired angular relationship with respect to the vehicle as the boom assembly is being raised or lowered would be desirable. The system should also be capable of automatically prohibiting the bucket from being rolled back to positions at which the load may spill over the back of the bucket.
A control system which permits the operator to select any desired position to which the bucket can be returned would also be desirable. In addition, the system should be capable of returning the bucket to the desired position from either direction of travel. A control system which also prohibits unnecessary wear on the tilt cylinders when the bucket is banged at the end of its cylinder stroke, yet still permits banging, would help extend the life of the cylinders. The control system must, of course, be relatively inexpensive and reliable to be commercially feasible. It would also be useful if the control system could be implemented along with existing hydraulic control systems. The hydraulic system should also be capable of manual actuation should any elements of the control system fail for any of a variety of reasons.